As consumers demand guaranteed performance of double glazed windows, manufacturers of the windows similarly demand performance guarantees from their suppliers of the components which they employ to make the double glazing units. In this regard, the formulators of sealants used to seal the edge of the double glazing units are generally required to provide the units' manufacturers with assurances, if not guarantees, concerning the performance of the sealants. For a composition to be successful as a sealant useful in the manufacture of double glazed window units, it must be formulated to provide both short-term and long-term (i.e. at least 10 years, preferably at least 15 years, more preferably at least 20 years or more e.g. 25 years) bonding of the sealant to the glass. The short-term bonding properties of the sealant to the glass are important, as it is the sealant which holds the components of the unit together prior to the unit being fitted in a window. The long-term bonding properties of the sealant to the glass are important, as it is the sealant which renders the unit weatherproof (providing that it is properly glazed) and so determines the lifetime of the unit in service.
The short-term properties of the sealant tend to be directly related to the amount of adhesion promoter present in the formulation. However, as the sealant becomes weathered the adhesion promoter in the sealant degrades, which can lead to detrimental effects on the long-term properties of the sealant (such as its bond with the glass interface). An excess of adhesion promoter can adversely affect the short-term properties of the sealant. The long-term properties of the sealant tend to benefit in proportion to the amount of adhesion promoter incorporated in the formulation, and which may be higher than desirable for the ideal short-term properties. There is a very fine balance between the amount of adhesion promoter the formulator can include in the composition to obtain the optimum between the short-term and long-term properties of the sealant. The formulator has to resolve conflicting requirements arising from both the nature of the application itself and limitations imposed by the characteristics of the raw materials used so as to produce a viable, balanced composition. In view of this fine balance, the glass sealant formulator is very reluctant indeed to make even minor adjustments to the amount of adhesion promoter employed in the sealant composition. Typically, a sealant will incorporate from 0.25 to 2.5 wt % adhesion promoter.
The formulations of compositions suitable for use as sealants useful in the manufacture of double glazing window units have developed over time, as formulators have obtained experience of the short-term and long-term performance of their products and the effects that varying the components and amounts thereof has on performance.
Whilst artificial weathering conditions may provide formulators with the ability to predict the long-term bonding properties of a particular sealant formulation, they tend to rely upon their actual experiences of the true performance of their products before they are prepared to give their customers written guarantees or other forms of assurances regarding the long-term performance of their products. This attitude has tended to make not only the glass sealant formulators but their customers as well very conservative and reluctant to change for fear of breaching their assurances, particularly with regard to the long-term performance properties of their products.
Glass sealants are generally complex formulations which tend to be flexible, substantially non-tacky solids at room temperature (18-20° C.). As the sealants are heated, for example up to their processing temperatures, which are typically more than 135° C. up to 220° C., e.g. 180° C., their physical characteristics slowly change from flexible, substantially non-tacky solids to very tacky, generally highly viscous fluids or pastes. Although the sealants demonstrate a softening point or range at temperatures from 0° C. to 220° C., under pressure during application they simply become more fluid as temperatures increase. The properties of the glass sealants make application of the compositions particularly difficult. Although such glass sealants are often commonly referred to as “hot melt” sealants, at no time do the formulations melt per se to form thin mobile liquids, for example as would be generally observed with a hot melt adhesive used in packaging. Although the glass sealants are substantially non-tacky solids at room temperature, they tend to adhere to surfaces when contacted with them for more than just a few seconds. This property of “blocking” leads to handling and storage problems, especially for storage at high ambient temperatures. Accordingly, historically, glass sealants have been supplied to manufacturers of double glazing window units in cardboard boxes which are either lined with silicone release paper or coated with a silicone resin. Either mode of packaging is expensive but, as it is more time consuming and labor-intensive to use silicone release paper, glass sealant formulators prefer to package their products in cardboard boxes coated on the lining with silicone resin.
Once the manufacturer of double glazing window units has removed the glass sealant from the packaging, the packaging is discarded. Being non-recyclable, the silicone coated cardboard is usually disposed of into land-fill sites. For environmental reasons, however, such form of disposal is highly undesirable. U.S. Pat. No. 5,373,682 discloses a method for the tackless packaging of hot melt adhesive. The method comprises pumping or pouring molten hot melt adhesive in liquid form into a cylindrical tube of plastic film, sealing the molten hot melt adhesive filled cylinder and allowing it to cool and solidify. The outer surface of the tube of plastic film is in direct contact with cooled water. The adhesive is pumped or poured at a temperature at or above the melting point of the plastic film. Although the inventors state that the coating of the adhesive with a plastic film provided no detrimental effects, the results of Table 1 clearly indicate that in both tests the sample with film had reduced adhesive properties compared to the control.
EP-A-0957029 discloses a method for packaging e.g. a hot melt adhesive by a process in which a liquid adhesive is co-extruded into a protective sheath of non-adhesive material and then subjecting the extruded product thus formed to a solidification process.